As will be appreciated, there are various mechanisms in which a member must be actuated at regular intervals but must be capable of being disabled and then later again enabled to selectively eliminate regular actuation of the member when desired. One such mechanism is a gathering machine for printed signatures in which a signature gripper is normally actuated at regular intervals to feed signatures seriatim to a travelling signature gathering belt or saddle on a binding line. In this connection, the increasing popularity of demographic editions of periodicals as well as the need to publish catalogs which contain many pages applicable to all parts of the country and other pages applicable only to certain regions is now well recognized.
Because of this demand, it has become necessary to develop gathering machines in which certain signature grippers or sucker arms are selectively disabled and enabled in order that the binding line may receive signatures fed by those signature grippers or sucker arms only when desired
As suggested hereinabove, a signature gripper commonly comprises a sucker arm which is oscillated to contact a signature while under vacuum and then to swing away thereby pulling the signature which is later freed by release of the vacuum when it reaches the main drum of the gathering machine. Both the mechanical oscillation of the signature gripper or sucker arm and the regular actuation and release of the suction are accomplished by mechanisms which are a part of the overall drive system to thereby eliminate any timing problems In this connection, the valve which controls the vacuum ordinarily is moved between an open position which places the grippers under vacuum and a closed position which eliminates the vacuum at the grippers by appropriate means such as rotation of a cam shaft which is operated by the drive system.
In order to take advantage of this fact, I have already developed a simple but highly effective apparatus which is capable of selectively eliminating the regular connection of the signature grippers or sucker arm to a source of suction or vacuum. This system is fully disclosed and claimed in commonly owned U.S. Pat. No. 4,353,393 which issued on Oct. 12, 1982, and it is specifically directed to a selective shut-off for repetitively operated valves so that even though the signature grippers or sucker arm continue to oscillate, they are temporarily unable to feed signatures. While this has proven to be most effective for the intended purpose, I have discovered that the continual striking of the sucker cups of the signature grippers or sucker arm onto the signatures during a long shut-off period can have a tendency to compact the signature stack.
As a result, it has remained to provide a system for selectively disabling the operation of the sucker arm so that the sucker cups cannot strike the signature stack when disabled.